Hyperthyroidism in Pregnancy

Pregnancy-Specific Forms of Hyperthyroidism

Hyperemesis gravidarum is associated with biochemical hyperthyroidism, including undetectable TSH levels and elevated free thyroxine index (FTI), due to high hCG levels during the first trimester 1
Graves' disease is responsible for 95 percent of hyperthyroidism cases in pregnancy and represents the most common pathological cause 2, 3

TSH testing is the initial test for screening, with both TSH and free T4 (FT4) or free thyroxine index (FTI) performed in pregnant women with suspected hyperthyroidism 1
Diagnosis is based on elevated free thyroxine (FT4) level or free thyroxine index (FTI) with suppression of TSH in the absence of thyroid mass or nodular goiter 2
Clinical features to identify include tremors, nervousness, insomnia, excessive sweating, heat intolerance, tachycardia, hypertension, and goiter 2
Distinctive ophthalmic signs include eyelid lag or retraction; dermal signs include localized and pretibial myxedema (specific to Graves' disease) 2

Failure to use trimester-specific TSH reference ranges can lead to misinterpretation of thyroid function tests and underdiagnosis 1

Unless hyperthyroidism is treated adequately, pregnant women are at increased risk for severe preeclampsia, preterm delivery, heart failure, and possibly miscarriage 2, 3
Thyroid storm is a rare medical emergency affecting a small percentage of pregnant women with hyperthyroidism 2
Low birth weight in neonates can occur with inadequately treated maternal hyperthyroidism 2
Fetal thyrotoxicosis needs to be considered in women who have a history of Graves' disease, as antibodies cross the placenta 2
The possibility of neonatal immune-mediated hypothyroidism or hyperthyroidism is an additional concern due to transplacental antibody passage 2